Dynamics of water use in Hydrangea macrophylla and Gardenia jasminoides

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Daily water use (DWU) of two ornamental species was quantified by changes in plant weights. DWU of two Hydrangea macrophylla cultivars ‘Pia’ and ‘Fasan’ was similar, ranging from 50-300 mL/plant depending on plant size and environmental conditions. Gardenia jasminoides ‘Radicans’ DWU ranged from 50-560 mL/plant. Daily light integral (DLI) and vapor pressure deficit (VPD) were the most important environmental factors affecting DWU, with DWU increasing with increasing DLI and VPD. The combination of plant age, final leaf area, DLI, and VPD explained 68 to 91% of day-to-day variation in DWU. When grown in a gradually drying substrate, water use by H. macrophylla ‘Fasan’ started to decrease at a higher VWC (0.28 m3∙m‐3) than G. jasminoides ‘Radicans’ (0.20 m3∙m‐3). Plant water uptake stopped at a VWC of 0.16 m3∙m‐3 in ‘Fasan’ and 0.12 m3∙m‐3 in ‘Radicans’, indicating that ‘Fasan’ is less adept at extracting water from a drying substrate than ‘Radicans’.